The present invention relates to a modular high spatial resolution scintigraphic device with multiple independent photomultipliers and with extensible visualisation area.
In particular, functional imaging systems with small field of view (see U.S. patent applications Ser. Nos. 09/202,894 (now U.S. Pat. No. 6,242,744) and 09/202,790 (now U.S. Pat. No. 6,236,605) in the name of Alessandro Soluri et al.) can be applied in Nuclear Medicine as localisation and diagnostic devices, of reduced weight and minimum size, in order to identify neoplasias with high spatial resolution. Use of said devices can also find application in the scintigraphic analysis of small animals, in order to experiment new radio-marked antibodies, specific for particular pathologies. Another field of application relates to the guided localisation of prostate and breast lesions, in order to identify the areas with higher uptake to be subjected to bioptic sampling, to integrate current radiographic and/or echographic techniques. Such devices can find further applications in Astrophysics and in industrial non destructive test systems.
In particular, the main use of the device relates to locating tumour lesions, especially in those techniques that require an adequate spatial precision such as biopsies (prostate and breast) or in radio-guided or radio-immune-guided surgery. To remove a tumour lesion, the surgeon needs to identify its location and, for this purpose, he/she normally uses the results of diagnostic investigations performed previously with techniques known as RX, CAT scans, NMR and traditional Scintigraphy.
However at the moment of the operation, after xe2x80x9copeningxe2x80x9d the part, the surgeon may need to locate even more precisely the area to be cut or removed and, for this purpose, he/she can employ a so-called xe2x80x9csurgical probexe2x80x9d. After injecting into the patient a radio-pharmaceutical, which has the peculiarity of being fixed more specifically in tumour cells, the surgeon uses a probe to detect the gamma-rays emitted by the radioisotope, present in the molecules of the drug in the area examined at a given time. The probe is sensitive to the intensity and energy of the detected gamma radiation and provides analogue signals that are proportional to the radioisotope concentration measured in the region identified by a single channel collimator.
The detected signals are converted to digital form providing information, in a light or sound scale, about the intensity of the signals that fall within the selected energy window. The limitation is constituted by the impossibility of providing an image that describes the spatial map of the concentration of radio-pharmaceutical and that only provides the visualisation of the counts in the area identified by the collimator.
This technique can be replaced with the use of a scintigraphic device which, although its size is fairly reduced, nonetheless still has considerable bulk during the surgical operation. This information has a considerable advantage linked to the real time visualisation of any neoplastic lesions and the confirmation of their total elimination after the surgical removal. Moreover, non scintigraphic techniques exist which allow to locate the sampling areas for needle biopsy, but with limitations on the precision of the areas to sample. These techniques, essentially based on RX and echographic systems, do not use a functional analysis but rather a morphological one, so that biopsies are generally guided in a non specific way.
The limitations of current technologies are mainly due to the poor spatial resolution (about 1 cm) and to the considerable dimensions of current commercial gamma-cameras. Already the devices claimed by Soluri et al. (see U.S. patent applications Ser. Nos. 09/202,894 now U.S. Pat. No. 6,242,744) and 09/202,790), now U.S. Pat. No. 6,232,605) in addition to those claimed by Francesco De Notaristefani et al. (WO 96/37991), Sealock et al. (U.S. Pat. No. 5,783,829), Stan Majewski et al. (U.S. Pat. No. 5,864,141), Scibilia et al. (U.S. Pat. No. 6,021,341), propose improvements both in terms of spatial resolution and in terms of reduced size and weight. Nevertheless, in some applications, the required spatial resolution becomes a fundamental parameter, so it is necessary to improve spatial resolution. Already Soluri et al. have provided an alternative to traditional systems by flat gamma cameras with very limited dimensions. These devices are well suited for specific diagnostic applications, such as, Radio Immune Guided Surgery (RIGS), or Radio Guided Surgery (RGS), or Single Proton Emission Mammography (SPEM), and Positron Emission Mammography (PEM). These applications are only a minimal part of those possible, because single devices can find aplication also in radio guided biopsies, integrating current echographic and/or radiographic technique with scintigraphic ones.
One of the current limitations surely consists of the inability to retrieve the diagnostic information in the dead border zones between individual devices set side by side. In this case if the crystal covers a border area between two photomultipliers, both will see a portion of charge in correspondence with the existing border zone (dead zone). The ambiguity of the event in this case is not easy to forecast and consequently place a limitation to events that fall within the dead zone between neighbouring photomultipliers.
Another fundamental aspect is linked to the limitations imposed by the construction techniques of the Position Sensitive Photomultiplier Tubes (PSPMT). The various models of photomultipliers individually exhibit peripheral dead areas, having total dimensions that exceed the stated active area. This causes problems when photomultipliers set side by side and/or mutually connected are used (see Soluri et al.) in order to obtain flat devices, constituted by multiple individual elements. In these devices it is essential that the dead zone between two bordering photomultipliers be smaller than 8 mm, in such a way as to use the connections of the signals exiting individual photomultipliers to constitute a single sensitive collection area. The presence of photomultipliers dead zones sets an upper limit in coupling devices, with active area that is definitely smaller than the total sizes of the individual photomultipliers.
Therefore, one aim of the invention is to provide a scintigraphic system constituted by the coupling of modules with independent photomultipliers, and in which the Field Of View (FOV) is defined by the way in which the individual modules are spatially positioned, both covering coplanar and contiguous areas, and involving areas of more complex geometry. Reference is also made to a forecasting model (see Raffaele Scafe et al., copyrightxe2x80x94software no. 2100001) which allows, in particular, to optimise the components of modular scintigraphic devices (discrete, suitable for panel assembly and individually collimated), based on scintillating crystal arrays, optical guides, PSPMT and electronic balancing networks optimised by the linearity of spatial response in the FOV, in terms of detectability of lesions according to their depth, size and uptake. Essentially, many individual modules can be coupled, each of which has its own dedicated electronics for calculating the detected event position.
Another aim of the invention is to obtain appropriate electronics, to identify unambiguously which photomultiplier was involved by the single event, in order to reconstruct the distribution map of all events observed by the entire device (constituted by the set of individual modules). This independence of the individual modules in calculating the event position over the entire device thus constitutes a substantial innovation relative to the single charge collection surface proposed by Soluri et al. in the past (see U.S. patent applications Ser. Nos. 09/202,894 (now U.S. Pat. No. 6,242,744) and 09/202,790) (now U.S. Pat. No. 6,232,605) in which the individual anode wires belonging to each photomultiplier were connected with the contiguous ones.
A further aim of the invention is to propose an electronic that makes independent the individual detection modules, each with its own individual visualisation area, which uses a single system for digitising and acquiring the signals about single events and which allows an appropriate software to perform the spatial reconstruction of the map of the detected and validated events, starting from the knowledge of the spatial positioning of the individual independent modules.
The subject device can be designed and built using the forecasting model (Raffaele Scafxc3xa8 et al.) that enables to adjust the visualisation area for individual photomultipliers and, in the case of multiple devices, to consider the individual photomultipliers mutually independent, so that the event is attributed unambiguously to the photomultiplier that detected the interaction with the incident radiation.
Yet a further aim of the present invention is that of minimising the dead zones inside the FOV and at its periphery, increasing the active area of the device to coincide with the total photomultiplier area (when a single detection device is used), or the total multiple photomultipliers area (in the case of more complex devices constituted by several photomultipliers and mutually connected in panel assemblies).
Therefore, the invention, as it is characterised in the claims that follow, solves the problem of providing a modular high spatial resolution scintigraphic device with multiple independent photomultipliers and with extensible visualisation area, comprising in succession from an open end of a container coated with a shielding cladding starting from the source of the event to be detected:
a collimator made of a material with high effective atomic number, having internally a multiplicity of equal conduits of determined length, identified and separated by septa of a thickness suitable to the energy of the photons to be detected;
a scintillation crystal structure able to convert the radiation from the source being examined into light radiation;
a plurality of photomultipliers of the type with crossed anodes or crossed wires receiving the light radiation emitted by the scintillation crystal structure and generating electrical signals proportional to their intensity and identifying the position co-ordinates (XY) of the event;
electronic circuits to amplify and integrate the signals generated by the photomultiplier to determine the event position co-ordinates and the related energy, according to a resistive chain configuration or to a sum/weighted-sum configuration, for their subsequent transfer to an analog to digital converter and afterwards to a personal computer that processes them and displays on a monitor an image which, from a general point of view, is characterised in that it comprises:
a plurality of adjacent photomultipliers, each provided with its own independent electronic circuits for determining the position co-ordinates (X, Y) and the energy of the event detected by the respective photomultiplier, forming detection modules and generating respective synchronism signals;
a circuit for interrogating said respective synchronism signals drawn from the respective said electronic components determining the signal indicating the photomultiplier that detected the event;
an OR circuit for recognising the signal indicating the photomultiplier that detected the event transmitted by the circuit and enabling only a corresponding analogue switch (14) to transfer the signals carrying the position co-ordinates and the energy of the event from the enabled electronic components to an activated analog to digital converter A/D;
a PC-BUS for transferring the digital signals to an electronic processor to be displayed in the form of images by means of a specific software;
a system reset circuit that rehabilitates the interrogation and the OR circuits at the conversion completion to make them available and ready to recognise a subsequent event.